In the field of chemical mechanical planarization (CMP), a process known as “pad conditioning” or “pad dressing” is used to restore the surface of the polishing pad and remove surface glazing by dislodging particulates and spent polishing slurry from the pad. Pad conditioning also re-planarizes the polishing pad by selectively removing pad material so as to roughen the newly-exposed pad surface. Pad conditioning may be performed “ex-situ” (i.e., conditioning the polishing pad between wafer polishing cycles) or “in-situ” (i.e., concurrent with, or during, a wafer polishing cycle). In a typical prior art “in-situ” pad conditioning process, a fixed abrasive conditioning disk is swept across the pad surface to remove a small amount of pad material and accumulated debris, thus creating new asperities in the pad surface to allow for the free flow of the polishing slurry. The removed pad material and debris then combine with the used polishing slurry and are passively carried away from the pad.
In most typical in-situ conditioning arrangements, the abrasive conditioning disk is held within a rotatable arm (referred to as an “end effector arm” or “conditioning arm”) that sweeps the disk across a portion of the polishing pad not currently in use. One particular arrangement is described in detail in U.S. Pat. No. 7,052,371 issued to S. J. Benner on May 30, 2006, assigned to the assignee of the present application and herein incorporated by reference. FIGS. 1 and 2 illustrate an exemplary conditioning arrangement as taught by Benner, where FIG. 1 illustrates the arrangement in a top view, and FIG. 2 in a side view. As shown, a conditioning apparatus 10 (referred to hereinafter as “conditioner head 10”) is mounted on a motorized end effector arm 12 so as to allow conditioner head 10 to sweep back and forth across the surface of polishing pad 14 (illustrated by arc AB in FIG. 1). An abrasive conditioning disk 22, mounted on the bottom of conditioner head 10, dislodges agglomerated debris as head 10 sweeps across polishing pad 14. End effector arm 12 is configured to impart a predetermined downward force (denoted “F” and shown in FIG. 2) and rotational movement (denoted “R” and shown in FIG. 2) to the conditioning disk, where a motor 17 is used in this particular embodiment to both pivot end effector arm 12 in arc AB (or through any other appropriate translational movement) about a fixed shaft 18, and provide rotational motion R and downward force F to the conditioning disk. This particular arrangement is considered to be exemplary only, with other systems utilizing, for example, a stationary abrasive (in place of a rotating conditioning disk), or an abrasive structure that covers the full pad radius and thus does not need to “sweep” across the pad to provide the conditioning effect.
In the above-cited Benner arrangement, apertured conditioning disk 22 is used to both dislodge surface glazing from the polishing pad and evacuate the dislodged debris through the application of a vacuum force pulling through and around the apertures formed in conditioning disk 22. As shown in FIGS. 1 and 2, a vacuum force V pulls debris upward and evacuates the debris through a channel 25 and away from polishing pad 14. Apertured conditioning disk 22 itself is attached to conditioner head 10 by either a mechanical arrangement, or by a magnetic mounting device 24 that is disposed between conditioning disk 22 and conditioner head 10. It is important to the proper operation of the conditioning process that the apertured conditioning disk be properly aligned with the other components in the conditioner head. During operation, proper alignment between the pad and the removal features also allows for efficient evacuation of the debris from the polishing pad surface. Proper alignment is also important for the resultant planarity of the polishing pad, which is a major factor in improving wafer polishing uniformity and reducing defectivity.
In high volume industrial applications, there is a constant need to improve the CMP apparatus and processes inasmuch as planarization of a semiconductor wafer is repeatedly used during the integrated circuit fabrication process, where there is significant cost and effort expended before and during each planarization operation. Any quality problems associated with the planarization can result in multiple “die” or chips being lost, with up to an entire wafer needing to be discarded, which is certainly an undesirable event. While quality issues concerning conditioning and polishing need to be addressed, the associated issues of efficiency and expense cannot be ignored, where “quality” and “expense” are often areas of concern that are in tension.
For example, in order to remove an abrasive conditioning disk from the CMP structure (i.e., to replace the disk and re-qualify the process), the conditioning disk must be unscrewed, unfastened, and/or grasped by hand and pried away (e.g., with a blade) in order to break the magnetic or mechanical force and pull the disk away from the conditioner head. At times, this manual operation may be cumbersome and may shed unwanted particulates onto the polishing pad surface. In most cases there is little clearance between the end effector arm of the conditioner and the polishing pad itself. Additionally, since any process involving removal of the conditioning disk is most often carried out in a clean room environment where the personnel must where gloves (and possibly other awkward attire) that are cumbersome/clumsy and may lead to damage or misalignment of the disk, or the remaining components. Misalignment can lead to chatter, which can cause shedding in addition to the pad non-uniformity. Slurry build-up due to misalignment can also lead to large particle (agglomerate) polishing defects. Radial variations in the polishing pad surface (a common problem resulting from different wear rates due to differences in abrasive/pad relative speed differences) are further exaggerated when the conditioning disk is misaligned with the conditioner head. The state-of-the-art processing leaves a trough, or shallow center region, on the polishing pad (due to the above-described speed differences), which creates high wafer polishing force in both of the “thicker” regions on the pad (if the trough is amplified), or laden with particles for the reasons for the reasons described above, exaggerating wafer polishing defects and results in non-uniform (edge fast) polishing.
Another problem area is associated with the translational movement of the end effector arm itself. In conventional use, end effector arm 12 translates in the z direction (i.e. “up” and “down”) as it is raised and lowered during the conditioning process, where this translational movement is controlled by an actuator 20 located within the end effector arm. The diaphragm, or piston action of a conventional actuator has been found to be problematic, with the diaphragm exhibiting poor reliability. Additionally, conventional air cylinder pistons often require a force of greater than five p.s.i. to initiate the movement of the actuator (that is, to break the static force of the assembly and seal friction). Thus, in most cases, the applied downforce of the conditioning disk onto the polishing pad must overcome this initial frictional force, and thereafter provide a corrective force to bring the system to the proper setpoint. If the setpoint requires less than 5 p.s.i. to be maintained, the break-away force cannot easily be achieved. In some equipment, the lifting force is not supplied by positive pressure, but is instead supplied by a vacuum (negative force). This configuration cannot be used to reliably offset the weight of the end effector itself, or frictional components within the actuator, making low downforce (e.g., less than two pounds) conditioning impossible. The result of these prior art actuator problems can be over-conditioning/dressing of the polishing pad, as a result of the inability to consistently and repeatedly achieve low abrasive downforces. Alternatively, or additionally, such prior art systems may require increased maintenance associated with over-cycling of the actuator in a mode referred to as “partial pad conditioning”. The partial pad conditioning mode provides the ability to cycle the dressing of the pad between “on” and “off” phases during a conditioning operation in an attempt to reduce the pad wear rate. This mode is intended to compensate for the lack of low downforce, contiguous conditioning. Partial pad conditioning can also lead to non-uniform dressing as the start and stop locations of the process are not precisely controlled. This leads to lesser process capability, poorer quality control of the polishing operation and potentially to process control-related down-time.
Moreover, in swept conditioner applications, as the polishing pad begins to age and presents an uneven top surface, the end effector arm will need to pivot slightly or adjust to height differences as the conditioner head sweeps back and forth. The pivoting range is desired to be, in most cases, a total of no more than 10°, with the design parameter of “level” defined for the mid-life thickness of the polishing pad. Any mechanical drive components within the end effector arm must be able to move through this range, while maintaining proper alignment/engagement. Misalignment can lead to a variety of reliability and/or particle generation (polishing defects) problems.
Thus, a need remains in the art for an improved conditioning apparatus and method for use in a CMP system that provides increased reliability and simplified serviceability to further improve the overall operation of the CMP system in terms of polishing/conditioning quality, efficiency and reliability.